Halogenated hydrocarbon lubricants containing heat treated boron nitride



HALOGENATED HYDROCARBON LUBRICANTS CONTAINING HEAT TREATED BORON NI-TRIDE Charles E. Saunders, Silver Spring, Md., assignor to the UnitedStates of America as represented by the Secretary of the Navy NoDrawing. Filed June 13, 1956, Ser. No. 591,254

1 Claim. (Cl. 252-25) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention relates to halogenated hydrocarbon lubricants andmore particularly to additives for increasing the lubricating qualitiesof such lubricants.

This application is a continuation-in-part of my copending applicationSerial No. 213,037, filed February 27, 1951, now abandoned.

Many halogenated hydrocarbons, i.e. hydrocarbons wherein fluorine orchlorine atoms are attached to the carbon atoms of the hydrocarbonskeleton structure, have been prepared and have been found to have goodlubricating qualities. Of particular interest are the fluorocarbonswhich have been found to have high resistance to both thermaldecomposition and chemical reaction. Their high resistance to chemicalaction, complete lack of toxicity, resistance to thermal decompositionand the fact that when they do decompose no toxic products issuetherefrom make the use of fluorocarbon lubricants highly desirable forspecialized applications. Air compressors, for example, now need to becarefully designed so as to prevent explosions due to combustion of theconventional petroleum oils used as lubricants. When fluorocarbonlubricants are utilized in these compressors not only is the fire hazardreduced because of the low combustibility of the lubricants but becauseof the resistance of these lubricants to oxidation the compressors maybe used in the presence of such highly oxidized gases as oxygen andchlorine. Of particular interest in this regard is the development of alubricant suitable for use in equipment utilizing high strength hydrogenperoxide. The primary interest at present is in the development of aperoxide pump lubricant. The violent oxidation characteristics ofhydrogen peroxide eliminate the possibility of using conventionalpetroleum lubricants and most of the available synthetic lubricants. Ofthe commercially available lubricants only the fluorocarbons were foundto be compatible with hydrogen peroxide. However the halogenatedhydrocarbon lubricants and particularly the fiuorocarbons whilepossessing the aforementioned desirable characteristics have lubricitycharacteristics which do not compare favorably with the lubricitycharacteristics of the highly developed petroleum lubricants.

Attempts have therefore been made to improve the lubricitycharacteristics of the fiuorocarbons and the other halogenatedhydrocarbons by the incorporation of suitable additives. Conventionalpetroleum oil additives were found to be unsuitable either because theadditives were not compatible with strong oxidizing agents such ashydrogen peroxide or because stable suspensions of the additives in thehalogenated hydrocarbon lubricants could not be obtained without greatdifficulty.

It is, therefore, an object of the present invention to provide anadditive for halogenated hydrocarbon lubrinited States Patent O2,960,460 Patented Nov. 15, 1960 cants which greatly increases theirlubricity and antiwear characteristics.

Another object is to provide an additive for halogenated hydrocarbonlubricants which is compatible with strong oxidizing agents.

A further object is to provide a method of producing an improvedadditive for increasing the lubricity characteristics of halogenatedhydrocarbon lubricants.

A still further object is to provide a method of preparing improvedhalogenated hydrocarbon lubricants.

Other objects and the attendant advantages of the invention will becomeapparent to those skilled in the art as the invention is disclosed inthe following detailed description.

The foregoing objects and the attendant advantages of the invention maybe accomplished through the addition of a small quantity of heat treatedboron nitride to the halognated hydrocarbon lubricant. It has been foundthat heat treated boron nitride is easily dispersed in these lubricantsand that the addition of a small quantity in the order of 0.75% willincrease the lubricity of the lubricants to a marked degree.

Boron nitride if prepared at a low temperature ap pears as a colorlessamorphous gelatine which dries to a hard brittle mass. In this state theboron nitride provides some improved lubricity to the halogenatedhydrocarbon lubricants but is chemically reactive. However, I have foundthat if the amorphous boron nitride is first heated to a hightemperature, i.e. about red heat, and allowed to cool slowly itscapability of increasing the lubricity of the halogenated hydrocarbonlubricants is greatly increased. Upon being heated to red heat, at about2500 C., the boron nitride takes on a dark color and appears to assume amore rigid crystalline structure which is practically insensitive tochemical action. This heat treated boron nitride was found to disperseeasily in the fluorocarbon lubricants and to be greatly superior toother suggested additives such as Molykote (molybdenum disulfide),graphite or Liqui-Moly (molybdenum disul-fide plus a solvent) inimproving the lubricating qualities of the aforementioned lubricants.

Wear tests have been made of the fluorocarbon lubricants which werefound to be impact insensitive with hydrogen peroxide. Those lubricantsfound best for the purpose are the Fluorolube oils which are partiallyfluorinated hydrocarbons obtained from the Hooker ElectrochemicalCompany. The Fluorolubes are described by the manufacturer in HookerBulletin Nos. 15 and 30 as addition polymers of trifluorovinyl chloridebuilt up of a recurring unit which is (CF CFCl-). They vary from lowviscosity colorless oils through heavy oils to opaque grease-likematerials. They are complex mixtures and not single chemical species.The various grades are obtained through the distillation of the basicpolymer and vary in density from approximately 1.88 gm./cc. at 25 C. forthe lighter oils to approximately 2.0 gm./ cc. for the heavy greases.Fluorolube S and Fluorolube F8 are preferred for use with strongoxidizing agents. At normal temperatures these fluorocarbons arewater-white, colorless, mobile liquids. Fluorolube FS has a meltingpoint of -60 C. and a density at F. of 1.86 gm./cc., viscosity 5centistokes. Fluorolube S has a melting point of 15 C. and a density at100 F. of 1.93 gm./cc.,, viscosity 100 centistokes similar in viscosityto SAE 30 oil. Other lubricants, such as the Kel-Flo polymer oils whichare lubricants similar to Fluorolubes manufactured by the M. W. KelloggCo. and Perfluorolube oils which are completely fluorinated hydrocarbonsmanufactured by the E. I. du Pont de Nemours Corp., may also be used ifdesired.

The testing machine used to evaluate these oils was aconstant speed(1800 r.p.m.) electric motor with a hardened steel wheel attached to theshaft. The wheel was 1% in. in diameter and had a radius of thickness ofinron the working. surface. This wheel was hardened to Rockwell 58c. Themotor was attached to a base plate which also holds a lever arrangementthat permits loading of the test piece. The test pieces are cold rolledsteel /1 x 2 x 4 The loading was accomplished by using the leverarrangement to force the test piece against the wheel. A :1 lever ratiogave a 20 pound loading at the point of contact. The tested lubricantwas fed from a drip oiler so the oil just contacted the edge of thewheel as it was fed. The samples and test wheel were finished with No.LN3 crocus cloth and cleaned prior to each run. The test was started byallowing the oil to completely cover the sample and to flow at a certainarbitrary drip rate (90 drops per min.) which was maintained for theduration of the run. The test was started by allowing the sample to comeinto contact with the wheel at a controlled rate. At the instant thewheel and sample came into contact the time measurement was started andthe test allowed to run for 5 minutes. The test was secured by removingthe sample from contact with the wheel and turning oil? the motor. Ifduring the run the drip oiler ran low on oil the oiler was refilled asoften as necessary to enable the test to run to completion. Theresultant length of mark on the test sample served as a comparativemeasurement of the quality of the lubricant tested.

Boron nitride which will pass through 'a 325 mesh screen may besuspended in the Fluorolube oils without difliculty. In this the boronnitride is superior to graphite and molybdenum disulfide because theseadditives require the addition of oleic acid as a dispersion agentbefore they can be suspended in the lubricant. The boron nitriderequires only a slight agitation to achieve suspension in Fluorolube S.Oleic acid may also be added to the boron nitride to assist in achievinga suspension in Fluorolube PS and other halogenated hydrocarbonlubricants.

To render the boron nitride hard and insensitive to chemical action andto increase the lubricating characteristics in "accordance with thisinvention the boron nitride must be heated to a temperature near butbelow the melting point. The boron nitride may be heated in a crucibleby a blast gas-flame to approximately 2500 C. When so heated the boronnitride darkens and hardens without igniting or burning. The boronnitride is maintained at the high temperature until the whole massassumes the dark coloration. Ten minutes has been found sufiicient timefor small quantities. This treatment results in the transformation ofthe white, gray or colorless amorphous boron nitride into a hard, dark,material having a six-sided tabular crystalline structure. The heattreated boron nitride is chemically inert not being attacked by acids oralkali at high temperatures and is not ignited when heated to hightemperatures in an atmosphere of hydrogen. As little as 0.50% by weightof this heat treated boron nitride greatly increases the lubricitycharacteristics of halogenated hydrocarbon lubricants such as thefluorocarbons.

Table I shows the results obtained by the above described wear test asapplied to petroleum oils, Fluorolube oils and Fluorolube oils with asmall part by weight of heat treated boron nitride added thereto forcomparison.

Table I Wear Mark in In. Lubricant Composition Test; I Test II From thetest results given in Table I it may be seen that the addition of asmall percentage by weight of the heat treated boron nitride to theFluorolube oils reduced the wear mark by as much as 42%.

From the foregoing detailed description it may be seen that there hasbeen provided an additive which greatly increases the lubricatingqualities of the halogenated hydrocarbon lubricants and which ischemically inert and resists oxidation in the presence of strongoxidizing agents at high temperatures. This additive makes possible theuse of the fluorocarbon lubricants and other halogenated hydrocarbonlubricants in the presence of strong oxidizing agents such asconcentrated acids, hydrogen peroxide, ozone, etc. as may be encounteredin the propulsion units of torpedoes, submarines, rockets, guidedmissiles and the like with greatly improved results.

The present invention is not to be considered as limited by any of theexamples described herein which are given by way of illustration only,but is to be limited solely by the terms of the appended claim.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

The method of improving the lubricity characteristics of a halogenatedhydrocarbon lubricant which comprises; heating boron nitride to a redheat, slowly cooling the boron nitride, adding to the lubricant fromabout 0.5 to about 0.75 percent by weight of said boron nitride.

References Cited in the file of this patent UNITED STATES PATENTS2,156,803 Cooper May 2, 1939 2,411,159 Hanford Nov. 19, 1946 2,467,145Morway et al. Apr. 12, 1949 2,551,639 Feasley et a1 May 8, 19512,628,196 Coonradt et a1. Feb. 10, 1953 FOREIGN PATENTS 12,377 GreatBritain of 1913 OTHER REFERENCES The Fluorocarbons, ChemicalEngineering, July 1950, pages 129-136.

Boron NitrideAn Unusual Refractory, Amer. Ceramic Soc. Bulletin, vol 31,#4 (1952).

